Question

How many grams of potassium carbonate are needed to make 200 ml of a 2.5 m solution?

Answer 1

Molarity = moles /volume

Moles = x/138

Volume = 200/1000 litre.

So,

2.5 = x/138×1000/200

2.5×138×200/1000 = x

x = 69gms.

Answer 2

The mass of potassium carbonate needed is 69.1 grams

Explanation:

To calculate the molarity of solution, we use the equation:

$\text{Molarity of solution}=\frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{Volume of solution (in mL)}}$

Molarity of solution = 2.5 M

Molar mass of potassium carbonate = 138.2 g/mol

Volume of solution = 200 mL

Putting values in above equation, we get:

$2.5M=\frac{\text{Mass of potassium carbonate}\times 1000}{138.2\times 200}\\\\\text{Mass of potassium carbonate}=\frac{2.5\times 138.2\times 200}{1000}=69.1g$

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